The color of flower is a particularly important character in ornamental plants, and flowers having various colors have been produced by cross breeding heretofore. However, when only a specific character such as flower color is introduced into a specific variety by cross breeding, because of uncertainty of cross breeding, it is necessary to repeat backcrossing over several generations, and a lot of effort and time are required. Further, a period of cross breeding varies depending on plant species, and in the cases of orchids such as moth orchids, which take a long time for blossom, it is practically impossible to produce a variety with a desired character only by cross breeding. Therefore, despite the demand of the market, it has been extremely difficult to change the flower color of a moth orchid to a desired color.
In recent years, it is possible to hybridize different species or genera by recombinant DNA technology, and it is expected to produce a new variety having a color which cannot be obtained by the conventional cross breeding.
The color of flower derives mainly from three types of pigments: anthocyanin, carotenoid and betalain. Among them, anthocyanin is the pigment having the broadest maximum absorption wavelength range and governs colors from red to blue. Anthocyanin is a kind of flavonoid and biologically synthesized through a metabolic pathway shown in FIG. 1. The color of anthocyanin substantially depends on its chemical structure, especially on the number of hydroxyl groups on the B ring. The hydroxylation of the B ring is catalyzed by a flavonoid 3′-hydroxylase (F3′H) and a flavonoid 3′,5′-hydroxylase (F3′5′H). When there is neither F3′H activity nor F3′5′H activity in petal cells, pelargonidin (orange) is synthesized, and when there is F3′H activity, cyanidin (red) is synthesized. Further, when there is F3′5′H activity, delphinidin (blue) is synthesized. Therefore, in order to produce the red flower color, the role of F3′H is considered to be important.
In a case of genetic alteration of flower color, a blue rose was produced using a F3′5′H gene from viola×wittrockiana (Patent Document 1).
On the other hand, alteration of the flower color of a moth orchid from pink to magenta by overexpressing an endogenous gene was reported (Non-Patent Document 1).
Patent Document 1: WO2005/017147
Non-Patent Document 1: Su and Hsu, Biotechnology Letters (2003) 25: 1933-1939.